Once thought to be just a messenger that allows genetic information encoded in DNA to direct the formation of proteins, RNA (ribonucleic acid) is now known to be a highly versatile molecule that has multiple roles in cells. It can function as an enzyme, scaffold various subcellular structures, and regulate gene expression through a variety of mechanisms, as well as act as a key component of the protein synthesis and splicing machinery. Perhaps most interestingly, increasing evidence indicates that RNA preceded DNA as the hereditary material and played a crucial role in the early evolution of life on Earth.